In a conventional radio telephone set, a received digital signal is converted to an analog signal in a codec included therein, when the talking mode is designated by an operator, and the analog signal is supplied to a telephone set circuit which is connected to an external terminal thereof, so that a talking between a caller and a callee is carried out.
On the other hand, when the digital communication mode is designated by the operator, a received digital signal is directly supplied to a personal computer or a facsimile apparatus which is connected to the external terminal without passing through the codec, so that the digital signal is processed in the personal computer or the facsimile apparatus.
In the conventional radio telephone set, however, there is a disadvantage in that a state in case where a digital signal is presently received in the non-talking mode is not externally indicated, for instance, in accordance with audio representation or visual display. Consequently, an operator who wants to make a telephone call can not know the mode state before his call is denied connection to the telephone line.